U.S. Pat. No. 5,242,390 discloses a method and apparatus for thermally ablating the lining of the uterus (known as the endometrium). The patented apparatus comprises a hysteroscope having a proximal portion for insertion into the uterus through the vagina, and a distal, gripping, visualization portion. The hysteroscope comprises both optical means for viewing the uterine cavity and channel means for delivering tissue-coagulating, controllably heated liquid into the cavity, as well as thermal insulation means for the hysteroscope. The thermal insulation means insulates the other body structures from the potentially damaging heat of the liquid during the period of the heated liquid transport and the coagulating surgery with the liquid so as to avoid thermal damage to tissue other than the endometrial tissue (such as vaginal tissue and endocervical tissue). The apparatus also includes liquid supply means for transporting the liquid through the channel means into and from the uterine cavity, and control means for regulating the temperature and pressure of the heated liquid.
The method of the patent as described therein includes the steps of: (a) distending the uterine cavity with a physiologically compatible aqueous solution (such as saline solution or other suitable liquid) under direct vision by means a hysteroscope having channel means for delivering and introducing liquid to the uterine cavity under pressure sufficient to inflate and directly expose the entire endometrial surface; (b) confirming that the proximal portion of the hysteroscope is properly located within the uterine cavity by appropriate visualization of its internal architecture; (c) withdrawing the aqueous solution from the uterine cavity, thus causing it to become substantially collapsed; and (d) distending the thus collapsed uterine cavity under direct vision by means of said hysteroscope by delivering and introducing to the uterine cavity aqueous carbohydrate solution (or a suitable equivalent solution) heated to an endometrial tissue-coagulating temperature under pressure sufficient to directly expose the entire endometrial surface and for a time sufficient to keep the heated solution in contact with the entire surface and, thereby, cause uniform and complete destruction of the endometrium.
The patent discloses a liquid supply means to the hysteroscope in the form of a syringe barrel and plunger containing heated liquid which is manually injected into the inlet port of the hysteroscopic sheath. The fluid which exits out of the uterine cavity and back through said channel and port of the sheath is circulated into a waste reservoir. Optionally, a separate supply of cold liquid is available, also in the form of a syringe barrel and plunger. Various valves are disclosed to control the ingress and egress of the various liquids.
Certain problems can arise during such surgical procedures, particularly if the patient absorbs a quantity of the heated liquid into her circulation (or fallopian tubes) during the installation of the heated solutions. During other types of hysteroscopic procedures, patients have been known to absorb large quantities of the liquid (as much as 2,000 or 3,000 cc) which can cause serious complications, up to and including death. Obviously, it is extremely important to closely monitor the amount of liquid being used to perform the procedure in order to ensure that no significant amounts are being absorbed. The fluid delivery system disclosed in U.S. Pat. No. 5,242,390 does not really provide any practical way of performing such monitoring.